The properties of polymers depend upon the properties of the catalyst used in their preparation. Therefore, a catalysts' composition, activation conditions, size, size distribution, shape, and the like, all factor into the characteristics of the final product and help ensure a good commercial workability of the catalyst, especially in gas phase and slurry polymerizations. For example, in order to produce olefin copolymers of about 500 μm in size, a catalyst particle size of about 15 μm to about 50 μm is generally preferred for the polymerization. Other physical properties such as a well-developed system of pores throughout the catalyst structure and good mechanical properties that resist wear during the polymerization process can be advantageous, with the latter helping ensure a good bulk density of the resulting polymer. Chemical features such as the ratio of polymerization-active metal(s) to co-catalyst or activator can affect active site structure, which in turn can impart a variety of properties to the polymer.
One aspect in developing polymerization catalysts is the search for new catalysts and methods for their production that allow a measure of control and adjustment of the composition, structure, size, and size distribution of the catalyst particles. One simple technique for preparing and shaping polymerization catalysts is spray-drying, a process in which liquid droplets containing dissolved or suspended materials, or both, are ejected from a flywheel or a nozzle, and the solid catalyst particles are formed as the dissolution or suspension solvent evaporates. The properties of spray-dried solid catalyst particles often may be adjusted by altering the make-up of the precursor solution or suspension, the spray-drying parameters, and the subsequent processing steps.
Another aspect in developing polymerization catalysts is the search for new catalysts and methods for their production that afford flexibility over the composition and structure of the catalyst and that of the resulting polymer.